Glycylproline is an end product of collagen metabolism that is further cleaved by prolidase (EC 3.4.13.9); the resulting proline molecules are recycled into collagen or other proteins. Prolidase deficiency is a rare autosomal recessive disease characterized by chronic ulcerative dermatitis, mental retardation, frequent infections and massive urinary excretion of iminodipeptides. The disease has been confirmed to be due to hereditary prolidase deficiency. It has been reported that the activity of the enzyme against glycylproline (Gly-Pro) is almost totally deficient in patients with prolidase deficiency, whereas the activity against other substrates is not so deficient. Some patients with prolidase deficiency have a marked urinary excretion of the iminodipeptide Glycylproline. The urine from patients with pressure sores contains significantly more Glycylproline than the urine from the control (PMID: 16009141, 7629169, 1536787, 10582130).